The present invention relates to an improvement in a brake for stopping rotation of cutting blades of bush cutting machines.
A brake for a bush cutting machine is disclosed, for example, in Japanese Utility Model Laid-Open Publication No. SHO-51-53248 entitled xe2x80x9cRotary Cutter Stopping Device for Bush Cutting Machinexe2x80x9d, or in Japanese Utility Model Laid-Open Publication No. SHO-51-99039 entitled xe2x80x9cSafety Device for Bush Cutting Machinexe2x80x9d.
The rotary cutter stopping device of SHO-51-53248 has a pair of brake shoes provided on an outer periphery of a driven shaft, cam plates mounted to press the respective brake shoes. When grip of a brake lever is released, the cam plates are rotated by springs, pressing the brake shoes against the outer periphery of the driven shaft, thereby stopping the rotary cutter. The above rotary cutter stopping device, however, requires an operator""s constant operation of the brake lever, which is troublesome, when stopping the rotary cutter. Further, the device requires such components as a brake lever and wires, increasing the number of components and thereby increasing the production cost.
The safety device of SHO-51-99039 has brake linings provided proximately to an outer periphery of a clutch drum. When grip of a brake lever is released, the brake linings come into contact with the clutch drum, and a motor is stopped in response to a signal from a movable contact, thereby stopping the rotary cutter. This safety device, however, requires an operator""s constant operation of the lever, which is troublesome, when stopping the motor and the rotary cutter, deteriorating its operability. Further, the device has a rod connected to a linkage, extended through a clutch housing, a construction which requires the consideration of dust- and water-proofing of the through hole. Further, the device requires such efforts as checking and adjustment of the tensioning of the linkage connected to the lever, which efforts are troublesome.
It is therefore an object of the present invention to provide a bush cutting machine with improved drive operability and improved dustproof and waterproof properties, which can be produced at a relatively low cost.
According to an aspect of the present invention, there is provided a bush cutting machine which comprises: a motor; a centrifugal clutch designed to establish drive connection when a number of rotations of an output shaft of the motor exceeds a predetermined value; a blade driving shaft for transmitting a torque; a cutting blade mounted to a distal end of the blade driving shaft; the centrifugal clutch comprising a clutch drum provided on the blade driving shaft, a centrifugally pivotal member provided on the output shaft of the motor and housed in the clutch drum, and a clutch case connected to a motor housing for enclosing the pivotal member and the clutch drum; and an automatic braking mechanism housed in the clutch case and comprising a brake drum formed integrally within the clutch case, at least two centrifugal braking members pivotally mounted to the clutch drum in such a manner as to expand by a centrifugal force proportionate to the number of rotations of the clutch drum, and resilient members for biasing the braking members to the brake drum, whereby the braking members are brought into abutting engagement with the brake drum with decrease in the number of rotations of the clutch drum.
With the automatic braking mechanism thus installed in the clutch case, it becomes possible to make the braking members abut against the braking drum in accordance with the reduced number of rotations of the clutch drum. When the number of rotations decreases, the braking members press against the braking drum, whereby the clutch drum instantaneously stops rotating and the blade driving shaft and the cutting blade also stop. Thus, the operator does not need to manually control a brake lever to stop the blade driving shaft, leading to improved operability. Further, with the automatic braking mechanism installed in the clutch case, it is no longer necessary to provide in the clutch case a through hole for a wire or a rod for braking. This further leads to the advantage that dustproof and waterproof properties are improved. Furthermore, with the automatic braking mechanism installed in the clutch case, the need for mounting such components as a brake lever or a wire is eliminated, resulting in reduced production cost.
Desirably, the braking members are disposed around the brake drum in equidistantly spaced relation to each other, and the resilient members are provided to extend between adjacent two of the braking members. As a result, the weight of the braking members and the weight of the resilient members can be evenly distributed, thereby preventing unbalanced rotation. The braking members are synchronized to improve the braking properties.